1. Technical Field
The present patent relates to a test method for a semiconductor memory, and more particularly to a test method for detecting defects of a cell capacitor capacitance of a particular block in a semiconductor memory sharing a sense amplifier.
2. Description of the Related Art
Generally, a memory cell included in a semiconductor memory has capacitors and transistors each of which perform switching control between a capacitor and bit lines.
After manufacturing the semiconductor memory, a test for the semiconductor memory is performed such that data is recorded in each memory cell forming a block, which hereinafter is referred to as a memory cell block, and the recorded data read from the same memory cell block to check the state of the memory cell block.
The recorded data in the memory cell block is sensed by a sense amplifier commonly connected to the bit lines of two memory cell blocks. The sense amplifier amplifies the electric potential difference between electric potentials of (recorded) data output through a pair of bit lines over a predetermined voltage value. Here, if the electric potential difference between electric potentials of (recorded) data output through the two bit lines is less than a sensing margin, the recorded data may not be correct such that an error occurs.
When the semiconductor memory is manufactured such that a memory cell therein has its capacitor capacitance less than a normal value due to various reasons, a sufficient sensing margin sensible in the sense amplifier cannot be secured. As such, when a memory cell having capacitor capacitance smaller than a normal value is detected, it must be replaced with an additional memory cell or screened before being sold on the market.
In order to test for defects of a memory cell block based on capacitor capacitance of the memory cell, the conventional test method senses only output data of one of two memory cell blocks through a sense amplifier, in which the two memory cell blocks share the sense amplifier. Namely, while one memory cell block is opened not to be connected to the sense amplifier, the output data of the other memory cell block connected to the sense amplifier is sensed and amplified by the sense amplifier.
However, even though the memory cell has a cell capacitance smaller than a normal value and is thus defective, the conventional testing method cannot effectively detect the defective memory cell, as long as it does not have any process defect.
Also, the conventional testing method cannot reduce the burden of test time, because test time for a semiconductor memory is gradually increased in semiconductor development and production.